pK of Chemical Functional Groups

The dissociation constant (pK) is the pH at which 50% of a compound (functional group) is protonated. Following are some examples of Weak Acid and Weak Base Chemical Functional Groups and their approximate pK’s.

Acids	pK
Sulfonic Acid	<1
Phosphate Ester	2
Carboxylic Acid	2.5-5
Uracil	8
Sulfonamide	7-9
Guanine	2.2, 9.4
Phenol	8-10

Bases	pK
Pyridine	5
Analine	5
Amine	7-10
Imidazole	7